unbendable

Unbendable is a descriptive term used to indicate that an object or material resists bending when subjected to transverse loads. In everyday language it implies very high stiffness, but in technical contexts it is not a formal property; instead engineers refer to stiffness, rigidity, or the modulus of elasticity. The degree to which something is unbendable is relative, depending on geometry, material properties, and the magnitude and direction of the applied load.

In materials science, bending resistance depends on Young's modulus (modulus of elasticity), the cross-sectional moment of inertia, and the geometry of the item. For a beam, deflection under a given load decreases as E and I increase. The concept is captured by beam theory, wherein higher stiffness reduces bending strain and residual deformation. A truly unbendable material would approach infinite stiffness, an idealization not found in real materials.

Common examples of stiff, less bendable materials include certain metals and ceramics, such as steel and alumina, as well as carbon fiber composites. Polymers typically exhibit greater ductility and may bend more before failure. Some materials are bend-resistant in one direction but not another, due to anisotropy in structure or layering.

The term is also used metaphorically to describe a person with an unwavering resolve or a policy that is not easily altered by pressure. In such uses, unbendable connotes persistence rather than mechanical stiffness.

See also: rigidity, stiffness, ductility, brittleness.